Irreversible control



Feb. 12, 1935. E, R CHlLD 1,990,978

' IRREVERSIBLE CONTROLr Filed Aug. 2, 1935 FIG. 1.

30 control system.

Patented Feb. 12,1935 I v A UNITED sTATEs PATENT OFFICE IRREVERSIBLE CONTROL Edward R. Child, Kenmore, N. Y., assignor to Curtiss Aeroplane & Motor Company, Inc., a corporation of New York Application August 2, 1933, Serial No. 683,272

10 Claims. (Cl. 244-29) This invention relates to aircraft control syswith respectl to said parallel guides, and carries tems, and particularly to irreversible mechanisms rollers or other anti-friction devices to engage interposed in the `control connections of such a said guides and to constrain the controlled memsystem. ber to parallel movement along said guides. An

In that type of control mechanism wherein a angled link connects the friction block with the 5 push-pull rod is adapted to be moved to control controlled member, and is pivoted to said block other elements, it is frequently desirable to proand to said member. The angular relationship vide means whereby operation of the rod may o f the link with respect to the balance of the eect movement in the controlled members,lbut mechanism is such that it transmits motion of wherein forces applied upon controlled members the control rod to the controlled member, but 10 are prevented from reacting into the controlfrod. prevents transmission of motion of either the rod Such mechanism may be utilized in con'n ect ic') njV 'or the member in the reverse direction by jamwith the controls of aircraft, particularlybin' the.l ming the friction block against the guides. For mechanism provided for operating the ailerons aclearer understanding of the operation of the l5 of an aircraft. It has been found that underinvention, reference may be made to the an- 15 certain circumstances, the ailerons of an aircraft nexed drawing, in which: are apt to flutter, due to the action of the air Fig. 1 isl a plan of an aircraft wing showing forces upon them, such flutterbeing harmful in the relationship of the invention to an aileron that it interferes with proper control of the airand an aileron control system; l craft, and may cause high stresses in the struc- Fig. 2 is an enlarged plan of the irreversible 20 ture with the possibility of effecting a failure 'of control mechanism: parts. Flutter may be prevented by eliminating Fig. 3 is a side elevation of the irreversible the possibility of inadvertent Amovement of the control mechanism; 1 i ailerons and controlled members, by'the use of Fig. 4 is a section on the line 4--4 of Fig. 3; an irreversible mechanismin the control system. Fig. 5 is a section on the'line 5--5 of Fig. 3; and 25 An object of the invention islto provide an' lFig. 6'is a diagram showing'the distribution of irreversible control mechanism. forces onthe irreversible mechanism.

A further object is to', provide irreversible. Fig. 1 shows a Wing 10 having anaileron 11 means which may be incorporated in a push-pulll hinged thereto along the-line 12. The aileron carries a horn 13 to which is pivoted a tube 14, 30 Another objectfof the invention lis to provide which by fore and aft movement, may change the means for eliminating flutter in aircraftcontrol angular relationship of the aileron 1l with resurfaces. .1 spect to the wing 10. Movement of the tube 14 Still another object is to provide an irreversible is effected through a bell crank l5, to which is control mechanism which may be readily incor. pivoted a controlled member 16. The controlled 85 porated in the control system of an airplane. member 16 is connected with a control rod 17 A further object-isv to provide friction means through an irreversible mechanism 18 carried in for preventing the inadvertent movement of a brackets 19 attached to the wing spar 20. The controlled member due to external stresses imcontrol rod 1'7 is pivoted to a control stick 17a posed thereon. in any well known mannen-so that operation of 40 Still another object is to provide an irreversible lthestick 17a results in actuation of the aileron 11 y mechanism for use in connection with a: push for control of the aircraft. Referring to Figs. 2 pull control system, which is extremely simple -to 5, the mechanism 18 comprises a pair of spaced in operation, which is light in weight, and which parallel guides or tracks 21 and'22 carried by the may be readily incorporated in an existing pushbrackets 19, the latter being provided with open- 45 pull control system. ings 23 through which the rod 17 and the con- Briefiy, the invention includes an irreversible trolled member 16 are adapted to slide in parallel mechanism interposed in a control connection relationship with the guides 21 and 22. At the joining an aircraft control surface with a control end of the rod 17, a bearing block or shoe 24 1s device. Said mechanism comprises a pair of rigidly attached, the side faces of this block being spaced parallel guides between which a control formed to lie closely adjacent the guides 21 and rod is adapted to slide. A block is carried at 22. Frictional material such as brake lining, or an end of the control rod which may frictionally the like, may be attached to the side faces of engage one or the other of said guides. A conthe block 24, so that a higlrcoeicient of friction trolled member vor rod is also adapted to slide may inhere when the block 24 engages with one 55' or the other of the guides. The controlled member 16 terminates a short distance from the inner end of the block 24, and has attached thereto a pair of triangular plates 25 and 26. The outer corners of these triangular plates, .which embrace the tracks 21 and 22, are joined by bushings 2'7 and 28 on vwhich rollers 29 and 30, are carried to engage theouterfsurfaces of the guides 21 and 22, thereby "allowing the controlledv member- 16, by itself, to be freely movable with respect Ito the guides 2l and 22. The bushing 28 carries a'freely swingable arm or link 31, extending-inwardly around the guide 22, and pivoted to the block 24 as at 32. The link 31 vis acutely angledwithre-j spect to the axis of the rod 17,' the'controlled member 16, and likewise with respect to the guides 21 and 22. Clearances in the severalpivots and between the several elements are.kept ,rather close so that, upon operation of the device, the

angularity of the link 31,with'respect to the other y parts changes `but little..

. persoon of the device, whiehfwiu be iater .analyzed in detail, is broadly as follows: Pushing .ofthe rod 17 toward the right, for instance, imposes `a force on. the link .31. The force4 is transmitted through the, link 3,1 to thevplates 25;.and

) ,thence tothe controlledmemberil, toeiect f .movement of the member 1 6 and, of the, parts to .which the-member is. connected. Reverse opera-l ,tion, whereinfafforce` is applied through the c ontrolled member 16to .the mechanism, is prevented, since such reverse forceimposes a force upon :the link 31 which presses the block. 24 against-the .1 guide 21 or theguide 22,. thereby frictionally bind.

ing said block against-the guide Atoprevent-.anyak lining .ag a inst .dry.steel,the cotangent ofthe movementlof themember 16 or of the control k.-rod1 '7. Forcesv mayf be applied I, in 1 either direction on the rod 1 7 to cause movementof the con- .trolled member, 16, but forces .in either direction applied on the controlled member -16yfail toproduceany movement in the ,control rod .17., and 1.

"pwiuhave to be,.appli ed,.along the axis of the likewise, holdthe member 16 frommoveifnent.v

A basic Irequirementuin the design of thismech anism -is a properrelationship between thefanglev which the link 31 .makes with the other members and the coeicient-of frictionbetweenthe .block 24 andthe guides:21 and `22; This-relationship basically is that the tangentof thefanglewhich the link .31 makes with theaxis of ,the rod 17 be greater thantheereciprocal of thefcoelcient of f. .friction betweenthe block 24 andgthe guides. 21v

and 22.- .Expressed inanother Wal/f the cotangent of the angle must vbalessthan` the coelcient of i Jfriction. c

An analysis of the forces--applied'onthe mechan ism will assist in clarifying. the operation .thereof, and reference may be made to, Fig. 6, wherein a compressive force R, acting through the link vcointo a horizontal component H, .tendinggto move the block 24 reversely.' or to the left, -andl likewise resolves into a vertical component which is opposed by-a' vertical force N.,actingy against the` block.- 'I'he force N is `that which determines the-l frictional resistance of the block against the guide 21, and engenders a, lfrlctional force F-vwhich resists movement of the-block. The coefficient of friction between the block 24 and the guide )21, -reprcsented by theletter f, is

equal-to.`

This hier ,Asan example,a ssurning a coefiicient of yfricf plied force R'will always be less than the friction force F, and hence, movement of the block is prevented. If an additional force P is applied to the 'block along the axis of the rod 1'7, the difference f, between or the sum of the force F and the force H may be overcome to cause movement of the block 2 4 along thef'gides 21 and 22 with resultant movement jof'lthe controlled member 16. The force R"niay be'applied in either direction with the same 'result/namely, binding of the block 24 against the guides 21 or 22 to prevent "movement thereof. The force P may be applied ineither direction, in a degree sumcient to overvcome eitherthe sum or difference of the forces F and H to cause movement of the block in either direction, regardless of the direction of action of the force R.

. vThe .above described relationship vof the ang-les 0 and a, resolves vinto the fact that thev available force F,must be greater than the horizontal component H of -the applied force R, which is embraced ,by.,the relation l bythe expression ACot0 f.

tionf'ogwhich be typical of a dry brake qmiislbegreaterihan approximates 63.5.

It -`will be ,appreciatedthat the vsmaller the diyergencebetween the coemcient of friction F andthe. ctangent ofthe angler, the less force controlF rod 17to.cause movement o f,.the condivergence should be', allowed between. the above named quantities so that :variations 4in the coeicient of friction may voccur without aecting i .tlielxcling:properties of the-mechanism.

It' will be appreciatedy that the irreversible .mechanismabove described is.; by 5o means lini-y 'ited inits} 'app1ication,.to aircraft control systems, but may be used in other applications.

,While I have describedmy invention in detail in. itspresent preferred embodiment, it will be obvious, tothosemskilled in vthe art, Aafter under- ,Standingmy invention, that various changesand lmodifications may be Imadetherein withoutde- 1. In a.control system khaving a control rod and a controlled member, a fixed track, ya,- shoe carried by said rod and slidable along said track, and a pivoted link connecting. said controlled member with said rod, said link-being so positioned relative toy saidrod that a line Joining thepivots.- thereon makes an'acute `angle with .said.rod. Y 2. In a control system, .a track, a control rod4 having a block adapted to slide along and fric- 'tionally engage said track, `a controlled member ...slidable along saidv track,land a link pivoted to said-controly rod and to said. controlled member.A

3. In a control system, a track, a control rod having a. block adapted to slide along and frictionally engage said track, a controlled member slidable along said track, and a link pivoted to said control rod and to said controlled member, said link being arranged to make an acute angle with said track.

4. In an irreversible control mechanism, a track, a control rod having a block for frictionally engaging said track, a controlled member, and a link pivoted to said control rod and to said member, a line through said pivots making, with the axis of said rod, an angle whose cotangent is less than the coefficient of friction between said bldck and said track.

5. In an irreversible control mechanism, a track, a control rod having a block for frictionally engaging said track, and a controlled element pivoted to said control rod and constrained to move therewith, said element making, with said rod, an angle whose cotangent is less than the coefficient of friction between said block and said track.

6. In an irreversible control mechanism having a control rod and a controlled member, a vblock carried by said control member, a pair of spaced parallel tracks between which said block is adapted to slide and with one or the other of which said block may frictionally engage, a controlled member having track engaging means, and an angled link pivotally connecting said block and said controlled member, the angle between said link and the line of travel of said block along said track having a cotangent less than the coeicient of friction between said block and said track.

7. In an irreversible control mechanism hav- 'ing a control rod and a controlled member, a track along which said rod and said member are constrained to slide and with which said rod may I frictionally engage, and an angled link articulated to said rod and to said member, said link making with said track an angle Whose tangent is greater than the reciprocal of the coecent of friction between said rod and said track.

8. In an irreversible control mechanism, a controlled member, a guide for said member, frictional means engageable with said guide, an element responsive in its action to forces applied to said member for causing engagement of said frictional means with said guide to prevent movement of said member, and a control rod connected to said member adapted to have a force applied thereto for overcoming said frictional means and for moving said member.

9. In an irreversible control mechanism for aircraft controls including a track, a control element slidable along and adapt-ed to frictionally engage said track, and a controlled member pivoted to said element and constrained to move therewith, said member being angularly organized relative to said track in such manner that the line of forced application from said pivot through said member makes an angle with vsaid track Whose cotangent is less than the coeflicient of friction between said element and said track.

10. In an irreversible control mechanism for aircraft controls including a track, a control element slidable along and adapted to frictionally engage said track, a controlled member pivoted to said element, and means for constraining said member at all times to an angle with said track Whose cotangent is less than the coeiiicientof friction between said element and said track.

EDWARD R. CHILD. 

